The Liquid Crystal Display (LCD) possesses advantages of thin body, power saving and no radiation to be widely used in many application scope, such as LCD TV, mobile phone, personal digital assistant (PDA), digital camera, notebook, laptop, and dominates the flat panel display field.
Most of the liquid crystal displays on the present market are backlight type liquid crystal displays, which comprise a liquid crystal display panel and a backlight module. The working principle of the liquid crystal display panel is that the Liquid Crystal is injected between the Thin Film Transistor Array Substrate (TFT array substrate) and the Color Filter (CF). The light of backlight module is refracted to generate images by applying driving voltages to the two substrates for controlling the rotations of the liquid crystal molecules.
In the active liquid crystal display, each pixel is electrically coupled to a thin film transistor (TFT), and the gate of the thin film transistor is coupled to a level scan line, and the drain is coupled to a vertical data line, and the source is coupled to the pixel electrode. The enough voltage is applied to the level scan line, and all the TFTs electrically coupled to the horizontal scan line are activated. Thus, the signal voltage on the data line can be written into the pixel to control the transmittances of different liquid crystals to achieve the effect of controlling colors and brightness. The Gate Driver on Array or GOA for short which utilizes the array manufacture (Array) process of the liquid crystal display panel at present to manufacture the gate row scan driving circuit on the TFT array substrate for realizing the driving way of scanning the gates row by row. The GOA technology can reduce the bonding procedure of the external IC and has potential to raise the productivity and lower the production cost. Meanwhile, it can make the liquid crystal display panel more suitable to the narrow frame or non frame design of display products.
With the development of the oxide semiconductor thin film transistor, such as Indium Gallium Zinc Oxide (IGZO) thin film transistor, the peripheral circuit around the panel based on oxide semiconductor thin film transistor also becomes the focus that people pay lots of attentions. The oxide semiconductor has higher carrier mobility but the threshold voltage thereof is about 0V and the subthreshold range swing is smaller, the voltage Vgs between the gate and the source of many TFT elements as the GOA circuit is in off state generally is 0V. Thus, the design difficulty of the GOA circuit based on the oxide semiconductor thin film transistor will be increased. There will be some function issues happening when the design adaptable to the scan driving circuit for the amorphous silicon semiconductors is applied to the GOA circuit based on the oxide semiconductor thin film transistor.
Besides, due to some external factor inductions and the stress effect, there will be a tendency that the threshold voltage diminishes toward minus value to the oxide semiconductor thin film transistor, which may directly result in malfunction of the GOA circuit for the oxide semiconductor thin film transistors. For example, at high temperature, the threshold voltage of the oxide semiconductor thin film transistor will move toward minus value to result in failure of the GOA circuit; similarly, under the function electrical stress function of light irradiation, the threshold voltage of the oxide semiconductor thin film transistor will move toward minus value. Therefore, the influence of the threshold voltage of TFT has to be considered as designing the GOA circuit based on oxide semiconductor thin film transistor.
FIG. 1 shows a circuit diagram of a GOA circuit based on oxide semiconductor thin film transistor focusing on the aforesaid issue according to prior art, comprising a pull-up controlling module 100, a pull-up module 200, a transmission module 300, a first pull-down module 400, a bootstrap capacitor module 500 and a pull-down holding module 600. However, there are still some certain problems remaining in the GOA circuit based on oxide semiconductor thin film transistor according to prior art. For example, N is set to be a positive integer and in the GOA unit circuit of the Nth stage, with the provided first constant negative voltage level VSS and second constant negative voltage level DCL, the issue of crossfire current exists for the GOA unit circuit of the Nth stage in the non-function period; the drain of the thin film transistor T75 in the pull-down holding module 600 is electrically coupled to the constant high voltage level DCH, and the constant high voltage level DCH will influence the pull-down holding of the first node Q(N) in the non-function period; besides, as showing respective frames, the residual charge exists at the first node Q(N), which can affect the normal output of the GOA circuit and result in the abnormal display of the image.